U.S. patent application number 13/024052 was filed with the patent office on 2011-06-02 for light source device and image display device having a wavelength selective element.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Fumika SUMIYAMA, Takashi Takeda.
Application Number | 20110128734 13/024052 |
Document ID | / |
Family ID | 39151007 |
Filed Date | 2011-06-02 |
United States Patent
Application |
20110128734 |
Kind Code |
A1 |
SUMIYAMA; Fumika ; et
al. |
June 2, 2011 |
LIGHT SOURCE DEVICE AND IMAGE DISPLAY DEVICE HAVING A WAVELENGTH
SELECTIVE ELEMENT
Abstract
A light source device includes: a plurality of light emitting
elements that emit laser light; and a wavelength selective element
that includes a light selective region functioning as a resonator
mirror of the light emitting element by selecting light of
predetermined selective wavelength from the laser light emitted
from one of the light emitting elements and reflecting the selected
light toward the light emitting element while allowing the
remaining laser light to pass therethrough, and a base member
having a plurality of the light selective regions so that the
wavelengths of the light selected by the light selective regions
are different from each other.
Inventors: |
SUMIYAMA; Fumika;
(Matsumoto-shi, JP) ; Takeda; Takashi; (Suwa-shi,
JP) |
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
39151007 |
Appl. No.: |
13/024052 |
Filed: |
February 9, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11892910 |
Aug 28, 2007 |
7905608 |
|
|
13024052 |
|
|
|
|
Current U.S.
Class: |
362/235 |
Current CPC
Class: |
H01S 5/4087 20130101;
H04N 9/3129 20130101; H01S 5/423 20130101; G02F 1/133621 20130101;
G01J 3/10 20130101; H01S 5/4025 20130101; G02B 26/001 20130101;
H01S 5/141 20130101; H01S 3/109 20130101; G03B 21/2026 20130101;
G02B 5/284 20130101; G03B 21/2053 20130101; H04N 9/3161 20130101;
G03B 21/14 20130101 |
Class at
Publication: |
362/235 |
International
Class: |
F21V 9/00 20060101
F21V009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2006 |
JP |
2006-236374 |
Jun 29, 2007 |
JP |
2007-172205 |
Claims
1. A light source device comprising: a plurality of light emitting
elements that emit laser light; a wavelength conversion element
that includes a light pass-through region through which the laser
light emitted from one of the light emitting elements passes, which
converts light of the wavelength included in the laser light into
light of a predetermined wavelength, and which emits the light
having been converted into the predetermined wavelength and light
having not been converted into the predetermined wavelength, and
that is constituted by a plurality of the light pass-through
regions so that the wavelengths of the light converted by the light
pass-through regions are different from each other; a wavelength
selective element that includes a light selective region into which
the light having been converted into the predetermined wavelengths
and the light having not been converted into the predetermined
wavelengths are incident, functioning as a resonator mirror of the
light emitting element by selecting the light having not been
converted into the predetermined wavelengths and reflecting the
light having not been converted into the predetermined wavelengths
toward the light emitting element while allowing the remaining
laser light to pass therethrough, and a base member having a
plurality of the light selective regions so that the wavelengths of
the light selected by the light selective regions are different
from each other; and a temperature variation section that varies
the temperature of each light selective region and that varies the
wavelengths of light selected by each light selective region.
2. The light source device according to claim 1, wherein the
wavelength conversion element has a domain-repetitive structure in
which polarization is repetitively reversed along the central axis
of laser light emitted from the light emitting elements, and a
width in the direction of the central axis of the laser light of
the domain is equal in all the light pass-through regions.
3. The light source device according to claim 1, wherein the
temperature variation sections are installed in the light selective
regions, respectively.
4. The light source device according to claim 1, wherein a peak
wavelength of light emitted from at least one of the light emitting
elements is identical to a peak wavelength of light selected in the
light selective region corresponding to the light selective
region.
5. An image display device comprising: the light source device
according to claim 1; a light modulating device that modulates
light emitted from the light source device in accordance with image
signal; and a projection device that projects images formed by the
light modulating device.
6. An image display device comprising: the light source device
according to claim 1; and a scanning section that scans the laser
light emitted from the light source device on a projection surface.
Description
[0001] This is a Division of application Ser. No. 11/892,910 filed
Aug. 28, 2007. The disclosure of the prior application is hereby
incorporated by reference herein in its entirety.
CROSS-REFERENCE TO RELATED APPLICATION
[0002] This application claims priority from Japanese Patent
Application No. 2006-236374, filed on Aug. 31, 2006, and Japanese
Patent Application No. 2007-172205, filed on Jun. 29, 2007, the
contents of which are incorporated herein by reference.
BACKGROUND
[0003] 1. Technical Field
[0004] The present invention relates to a light source device and
an image display device.
[0005] 2. Related Art
[0006] Discharge lamps such as extra-high pressure mercury lamps
are generally used as light sources in projection type image
display device in recent years.
[0007] However, in such a discharge lamp, there are problems in
that the service lifetime is short, instantaneous lighting is
difficult, the color reproducibility range is narrow, and the
ultraviolet rays emitted from the lamp may degrade the liquid
crystal light valve.
[0008] As an alternative to this discharge lamp, a projection type
image display device using a laser light source for emitting
monochromatic light is proposed here.
[0009] However, while a laser light source does not have the
problems mentioned above, the laser light source has the
disadvantage that it has coherence.
[0010] As a result, interference band appears as speckle noise on
the projection surface on which laser light is projected and the
image deteriorates. Thus, measures against speckle noise are
necessary if highly accurate images are to be displayed.
[0011] Devices in which dispersion elements are disposed on the
projection surface or in an optical system projecting laser light
on the projection surface, and devices that vibrate the dispersion
elements are well known as devices for eliminating speckle
noise.
[0012] For instance, an image display device including such a
device is proposed in the Japanese Unexamined Patent Application,
First Publication No. 2004-144936.
[0013] This image display device includes diffusion elements on the
surface of which uneven portions of specific shape are formed.
[0014] These diffusion elements are made to vibrate at a
predetermined frequency by an exciting device in the plane
perpendicular to the optical axis, thereby changing the strength
distribution of laser light incident onto the diffusion
elements.
[0015] As a result, the speckle noise can be suppressed.
[0016] Moreover, a high output laser is necessary in the light
source of a high intensity projector, and an array of light sources
is used for high output.
[0017] For example, in the Japanese Unexamined Patent Application,
First Publication No. 2004-144794, a method of controlling the
temperature of the array of light sources is proposed as a measure
against the speckle noise due to the array of light sources.
[0018] Each semiconductor laser in this array of light sources is
maintained at a different temperature in this image display device.
Each semiconductor laser emits luminous flux of varying wavelength
depending on the difference in temperature.
[0019] In this way, by varying the output wavelength, the coherence
of the semiconductor lasers can be reduced, and the speckle noise
of the entire output source can be reduced.
[0020] The image display device disclosed in the Japanese
Unexamined Patent Application, First Publication No. 2004-144936
has only one light source. If a plurality of light sources like an
array of light sources is used, light is diffused by identical
diffusion elements, so the coherence of light beams emitted from
multiple light sources can not be reduced.
[0021] Also, to vibrate the diffusion elements, an exciting device
is used. Therefore, the device on the whole increases in size, and
noise due to vibration is generated.
[0022] The image display device disclosed in the Japanese
Unexamined Patent Application, First Publication No. 2004-144794 is
based on the prerequisite that a light source that does not require
an external resonating structure, that is, a light source that
outputs laser light directly, is used.
[0023] Evidently, the speckle noise can be effectively suppressed
in case of a light source that does not require an external
resonating structure.
[0024] Here, the basic configuration elements of a light source
including external resonator are the light emitting element and
wavelength selective element (resonator mirror).
[0025] Even if a plurality of light emitting elements is used, a
wavelength selective element that selects a single wavelength is
generally used considering the cost benefits and the ease of
assembly.
[0026] For laser oscillation in the wavelength selective element,
the band of the wavelength selected needs to be narrow.
[0027] The result is that even if the wavelength of each light beam
emitted from an array of light sources is varied, as disclosed in
the Japanese Unexamined Patent Application, First Publication No.
2004-144794, a single wavelength is selected by the wavelength
selective element, and the coherence of the entire light source
including wavelength selective element does not decrease.
SUMMARY
[0028] An advantage of some aspects of the invention is to provide
a light source device, which is small in size, and in which it is
possible to suppress speckle noise, to reduce the coherence of
light beams, and to resolve the problems mentioned above. Also, an
advantage of some aspects of the invention is to provide an image
display device including the light source device.
[0029] A first aspect of the invention provides a light source
device including: a plurality of light emitting elements that emit
laser light; and a wavelength selective element that includes a
light selective region functioning as a resonator mirror of the
light emitting element by selecting light of determined selective
wavelength from the laser light emitted from one of the light
emitting elements and reflecting the selected light toward the
light emitting element while allowing the remaining laser light to
pass therethrough, and a base member having a plurality of the
light selective regions so that the wavelengths of the light
selected by the light selective regions are different from each
other.
[0030] In the light source device related to the first aspect of
the invention, in the wavelength selective element, a part of the
light of predetermined selected wavelength emitted from the light
emitting elements is reflected, oscillated and amplified between
the resonator mirrors, while the remaining laser light passes
through without amplification.
[0031] Some of the wavelengths of light that have passed through
the wavelength selective elements from the selected wavelengths
differ from other wavelengths and have been amplified. Therefore,
the light intensity is extremely strong.
[0032] At this stage, in the light selective regions on the base
member of the wavelength selective element, the wavelengths of the
selected light are different from each other.
[0033] As a result, even if the peak wavelength of light emitted
from the light emitting elements is the same, for example, the
light emitted from the light emitting element has bandwidth;
therefore light of different wavelengths is amplified and can be
extracted from this bandwidth.
[0034] That is, when the light emitted from each light emitting
element resonates in the light selective region of each of the
wavelength selective element, the wavelength of light amplified in
the resonator mirror structure emitted from each region
differs.
[0035] That is, according to the invention, unlike the conventional
item, since the wavelength selective element does not emit light of
a single wavelength, the wavelength region of light passing through
the wavelength selective element is assumed to spread over the
entire region.
[0036] As a result, the coherence of amplified light beams emitted
from each region of wavelength selective element reduces, and thus
the speckle noise can be suppressed.
[0037] There is no need to provide diffusion elements or exciting
devices for wavelength selective elements as in the past, therefore
the entire device can be reduced in size.
[0038] The peak wavelength of light emitted from each light
emitting element of the light emitting elements differs by a few nm
because of manufacturing error.
[0039] In this case, the light emitted from the light emitting
element can be efficiently extracted from the wavelength selective
element by using the wavelength selective element that has the
region selected by light of the same wavelength as the peak
wavelength of each light emitting element.
[0040] That is, since wavelength selective element that could
select only single wavelength was used in the past, variation
occurred in the plane of the light emitted from the light source
device.
[0041] However, according to the light source device of the
invention, light can be passed through without any drop in the
strength of the incident light because of the wavelength selective
element; therefore, the light utilization efficiency can be
improved.
[0042] It is preferable that the light source device of the first
aspect of the invention further include a strain application
section that applies strain to the light selective regions so as to
vary the magnitude of the strain on the light selective regions and
that varies the wavelengths of light selected by the light
selective regions.
[0043] The light source device related to the first aspect of the
invention, for example, a piezoelectric element may be used as the
strain application section to apply strain to the light selective
regions so as to vary the magnitude of the strain on the light
selective regions.
[0044] As a result, the lattice spacing in the wavelength selective
element varies, and the wavelength reflected in each region by the
wavelength selective element differs.
[0045] Accordingly, when light emitted from the light emitting
elements are reflected by the wavelength selective element and
resonance is caused, the light amplified and emitted from each
region will have different wavelengths.
[0046] Consequently, by using a simple configuration, the coherence
of light beams passing through each region of the wavelength
selective element reduces, costs can be reduced and speckle noise
can be suppressed.
[0047] the strain application sections may be installed in the
light selective regions, respectively.
[0048] In this configuration also, strain may be applied such that
the wavelengths of light selected by the light selective regions
are mutually different.
[0049] It is preferable that, in the light source device of the
first aspect of the invention, the strain application sections be
installed in the light selective regions, respectively.
[0050] In the light source device of the first aspect of the
invention, by providing a strain application section in each light
selective region, the strain applied in each region can be
varied.
[0051] As a result, the lattice spacing within each region of the
wavelength selective element can be adjusted.
[0052] Consequently, when variation exists in the light emitted
from the light emitting element, the selective wavelength can be
varied by region so as to match the wavelength of the light emitted
from the light emitting element.
[0053] That is, the light utilization efficiency can be improved to
enable the wavelength of light emitted from each light emitting
element to be aligned with the selective wavelength of each region
of the corresponding wavelength selective element.
[0054] It is preferable that the light source device of the first
aspect of the invention further include a temperature variation
section that varies the temperature of each light selective region
and that varies the wavelengths of light selected by each light
selective region.
[0055] The temperature variation section in the light source device
related to the first aspect of the invention varies the temperature
according to each light selective region of the wavelength
selective element; therefore, the lattice spacing within the
wavelength conversion element varies according to the temperature
of each light selective region.
[0056] As a result, in the light selective regions of the
wavelength selective element, the wavelengths of the selected light
are different from each other.
[0057] Accordingly, light emitted from the light emitting elements
is reflected at each light selective region of the wavelength
selective element and becomes light in which the wavelength
differs.
[0058] In this way, without applying any external force on the
wavelength selective element and with only a change in the
temperature of each light selective region, the periodic lattice
spacing within the wavelength selective element changes.
[0059] As a result, the coherence of amplified light beams
reflected from each region of wavelength selective element reduces
with a simpler configuration, and thus the speckle noise can be
suppressed.
[0060] Moreover, a plurality of temperature variation sections may
be provided, and a temperature variation section may be provided
for a set of multiple light selective regions.
[0061] In this configuration also, the temperature may be varied
such that the wavelengths of light selected by the plurality of
light selective regions are mutually different.
[0062] It is preferable that, in the light source device of the
first aspect of the invention, the temperature variation sections
be installed in the light selective regions, respectively.
[0063] In the light source device of the invention, by providing a
temperature variation section in each light selective region, the
temperature applied in each region can be varied.
[0064] As a result, the lattice spacing within each region can be
adjusted.
[0065] Consequently, when variation exists in the light emitted
from the light emitting element, the selective wavelength can be
varied by region so as to match the wavelength of the light emitted
from the light emitting element.
[0066] Accordingly, the wavelength of light emitted from each light
emitting element and the selective wavelength of each region of the
wavelength selective element can be aligned, and the light
utilization efficiency can be improved.
[0067] It is preferable that, in the light source device of the
first aspect of the invention, the wavelength selective element
include a wavelength selective film, and the wavelengths of light
selected by the light selective regions be different from each
other by varying a thickness of the wavelength selective film in
each of the light selective regions.
[0068] According to the light source device related to the first
aspect of the invention, the thickness of thin film with varying
refractive index formed on a substrate differs with the light
selective region of the wavelength selective element; therefore,
the wavelength of light selected for each light selective region
will vary with the wavelength selective element.
[0069] Consequently, when the light emitted from the light emitting
elements passes through the wavelength selective element, the
wavelength of light emitted from each light selective region will
differ.
[0070] That is, the wavelength selective element is formed by thin
film of film thickness that suits the selective wavelength;
therefore, there is no need to control the wavelength selective
element such that the selective wavelength in each selective region
of the wavelength selective element differs.
[0071] As a result, the coherence of amplified light beams
reflected from each region of wavelength selective element reduces
correctly with a simpler configuration, and thus the speckle noise
can be suppressed.
[0072] A second aspect of the invention provides a light source
device including: a plurality of light emitting elements that emit
laser light; a wavelength conversion element that includes a light
pass-through region through which the laser light emitted from one
of the light emitting elements passes, which converts light of the
wavelength included in the laser light into light of a
predetermined wavelength, and which emits the light having been
converted into the predetermined wavelength and light having not
been converted into the predetermined wavelength, and that is
constituted by a plurality of the light pass-through regions so
that the wavelengths of the light converted by the light
pass-through regions are different from each other; and a
wavelength selective element that includes a light selective region
into which the light having been converted into the predetermined
wavelengths and the light having not been converted into the
predetermined wavelengths are incident, functioning as a resonator
mirror of the light emitting element by selecting the light having
not been converted into the predetermined wavelengths and
reflecting the light having not been converted into the
predetermined wavelengths toward the light emitting element while
allowing the remaining laser light to pass therethrough, and a base
member having a plurality of the light selective regions so that
the wavelengths of the light selected by the light selective
regions are different from each other.
[0073] According to the light source device related to the second
aspect of the invention, when laser light of green color is to be
emitted, for example, a light source of wavelength 1060 nm is used,
and a wavelength selective element that allows light of green color
to pass through is used as the light emitting element.
[0074] As a result, the light emitted from the light emitting
element passes through the wavelength conversion element, and is
repeatedly reflected between the light emitting element and the
wavelength selective element.
[0075] Subsequently, the laser light converted into green color is
emitted from the wavelength selective element.
[0076] Thus light of the desired wavelength can be obtained from
the wavelength conversion element, and light can be emitted with
the speckle noise suppressed.
[0077] It is preferable that, in the light source device of the
second aspect of the invention, the wavelength conversion element
have a domain-repetitive structure in which polarization is
repetitively reversed along the central axis of laser light emitted
from the light emitting elements, and the wavelengths of light
converted by the light pass-through regions be different from each
other by varying a width in the direction of the central axis of
the laser light of the domain for each of the light pass-through
regions.
[0078] In the light source device of the invention, the wavelength
of light converted for each light pass-through region of the
wavelength conversion element differs because the polarization
reversal period in the direction of the optical axis of the light
passing through the wavelength conversion element differs for each
light pass-through region of the wavelength conversion element.
[0079] Accordingly, when light emitted from the light emitting
elements passes through a wavelength conversion element, the
wavelength of light emitted from each light pass-through region
will be different.
[0080] That is, the polarization period of each light pass-through
region of a wavelength conversion element may be varied
corresponding to the wavelength of light selected in each light
selective region of the wavelength selective element. Thus, the
wavelength of light converted in the wavelength conversion element
can be easily aligned with the wavelength of light selected in the
wavelength selective element.
[0081] As a result, a light source device in which speckle noise is
suppressed can be attained while light utilization efficiency of
light emitted from the light emitting elements can be improved by
using a simple configuration.
[0082] It is preferable that the light source device of the second
aspect of the invention further include a temperature variation
section that varies the temperature of each the light pass-through
region and that varies the wavelengths of light converted by each
light pass-through region. In the light source device, the
wavelength conversion element has a domain-repetitive structure in
which polarization is repetitively reversed along the central axis
of laser light emitted from the light emitting elements, and a
width in the direction of the central axis of the laser light of
the domain is equal in all the light pass-through regions.
[0083] In the light source device related to the second aspect of
the invention, the polarization reversal period along the optical
axis of light passing through each light pass-through region of the
wavelength conversion element is the same.
[0084] However, since the temperature is varied for each light
pass-through region of the wavelength conversion element by the
temperature variation section, the refractive index corresponding
to temperature varies for each light pass-through region.
[0085] As a result, the wavelength of light converted in each light
pass-through region of the wavelength conversion element
differs.
[0086] Accordingly, the wavelength of each light beam emitted from
the light emitting elements and passing through each light
pass-through region of the wavelength conversion element will
differ.
[0087] In this way, by merely varying the temperature of each light
selective region of the wavelength selective element, the internal
structure of a wavelength selective element can be easily
changed.
[0088] As a result, a light source device in which speckle noise is
suppressed can be attained while light utilization efficiency of
light emitted from the light emitting elements can be improved by
using a simple configuration.
[0089] It is preferable that the light source device of the second
aspect of the invention further include a voltage application
section that applies voltage to the light pass-through regions so
as to vary the voltage to the light pass-through regions and that
varies the wavelengths of light converted by the light pass-through
regions. In the light source device, the wavelength conversion
element has a domain-repetitive structure in which polarization is
repetitively reversed along the central axis of laser light emitted
from the light emitting elements, and a width in the direction of
the central axis of the laser light of the domain is equal in all
the light pass-through regions.
[0090] In the light source device related to the second aspect of
the invention, the refractive index will differ in each light
pass-through region of the wavelength selective element by varying
the applied voltage in the voltage application section of each
light pass-through region of the wavelength selective element.
[0091] In this way, by varying the voltage applied on each light
pass-through region of the wavelength conversion element, the
wavelength of light converted in each light pass-through region of
the wavelength conversion element can be made the same as the
wavelength of light passing through each light selective region of
the wavelength selective element corresponding to each region.
[0092] As a result, the wavelength of light converted in each light
pass-through region of the wavelength conversion element can be
made to differ.
[0093] Accordingly, a light source device that suppresses speckle
noise can be attained while improving the light utilization
efficiency of light emitted from the light emitting elements by a
simpler configuration.
[0094] It is preferable that the light source device of the second
aspect of the invention further include a strain application
section that applies strain to the light selective regions so as to
vary the magnitude of the strain on the light selective regions and
that varies the wavelengths of light selected by the light
selective regions.
[0095] According to the light source device related to the second
aspect of the invention, effects similar to the effects when the
strain application section mentioned above is provided, can be
obtained.
[0096] It is preferable that, in the light source device of the
second aspect of the invention, the strain application sections be
installed in the light selective regions, respectively.
[0097] Also, according to the light source device related to the
second aspect of the invention, effects similar to the effects
obtained when the strain application sections mentioned above are
provided, can be obtained.
[0098] It is preferable that the light source device of the second
aspect of the invention further include a temperature variation
section that varies the temperature of each light selective region
and that varies the wavelengths of light selected by each light
selective region.
[0099] Effects similar to those when provided with the
above-mentioned temperature variation section can be attained in
the light source device related to the invention.
[0100] It is preferable that, in the light source device of the
second aspect of the invention, the temperature variation sections
be installed in the light selective regions, respectively.
[0101] Effects similar to those obtained when the above-mentioned
temperature variation sections are provided, can be obtained in the
light source device related to the invention.
[0102] It is preferable that, in the light source device of the
second aspect of the invention, the wavelength selective element
include a wavelength selective film, and the wavelengths of light
selected by the light selective regions be different from each
other by varying a thickness of the wavelength selective film in
each of the light selective regions.
[0103] Effects similar to those attained when the thickness of the
above-mentioned wavelength selective film is different from each
other can be obtained in the light source device related to the
invention.
[0104] It is preferable that, in the light source device of the
second aspect of the invention, a peak wavelength of light emitted
from at least one of the light emitting elements be identical to a
peak wavelength of light selected in the light selective region
corresponding to the light selective region.
[0105] The wavelength of light converted in each light pass-through
region of the wavelength conversion element is the same as the
wavelength of light selected in each region of the corresponding
wavelength selective element in the light source device related to
the invention.
[0106] As a result, there is no reduction in the amount of each
light beam converted in each region of the wavelength conversion
element when passing through each light selective region of the
corresponding wavelength selective element.
[0107] Consequently, by using a simple configuration, the light
utilization efficiency of light emitted from the light emitting
elements can be increased, and the coherence of light beams passing
through each region of the wavelength selective element can be
reduced; therefore, the speckle noise can be suppressed.
[0108] A third aspect of the invention provides an image display
device including: the light source device of the first aspect or
the second aspect of the invention; a light modulating device that
modulates light emitted from the light source device in accordance
with image signal; and a projection device that projects images
formed by the light modulating device.
[0109] According to the image display device related to the third
aspect of the invention, light emitted from the light source device
is made incident on a light modulating device.
[0110] The image formed by the light modulating device is projected
by the projection device.
[0111] At this stage, the light emitted from the light source
device, is light with reduced coherence, as mentioned above.
Therefore, the light projected by the projection device is light in
which the speckle noise is suppressed.
[0112] Accordingly, a satisfactory image can be displayed.
[0113] A fourth aspect of the invention provides an image display
device including: the light source device of the first aspect or
the second aspect of the invention; and a scanning section that
scans the laser light emitted from the light source device on a
projection surface.
[0114] According to the image display device related to the
invention, light emitted from the light source device is scanned by
a scanning section.
[0115] The light scanned by the scanning section will be projected
on the projection surface.
[0116] At this stage, the light emitted from the light source
device is light with reduced coherence, as mentioned above.
Therefore, the light projected on the projection surface on which
it is to be projected is light in which the speckle noise is
suppressed.
[0117] Accordingly, a satisfactory image without uneven brightness
can be displayed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0118] FIG. 1 is a plan view of the light source device related to
a first embodiment of the invention.
[0119] FIG. 2 is a plan view of the light source device related to
a second embodiment of the invention.
[0120] FIG. 3 is a plan view of the light source device related to
a third embodiment of the invention.
[0121] FIG. 4 is a plan view of the light source device related to
a fourth embodiment of the invention.
[0122] FIGS. 5A and 5B are an output wavelength of a light emitting
element of the light source device of FIG. 4.
[0123] FIG. 6 is a plan view of the light source device related to
a fifth embodiment of the invention.
[0124] FIG. 7 is a plan view of the light source device related to
a sixth embodiment of the invention.
[0125] FIG. 8 is a plan view of the light source device related to
a seventh embodiment of the invention.
[0126] FIG. 9 is a plan view of the light source device related to
an eighth embodiment of the invention.
[0127] FIG. 10 is a plan view of the light source device related to
a ninth embodiment of the invention.
[0128] FIG. 11 is a plan view of an image display device related to
a tenth embodiment of the invention.
[0129] FIG. 12 is a plan view of examples of modification of the
image display device of the invention.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0130] The embodiments of the light source device and the image
display device related to the invention are explained here
referring to the drawings.
[0131] The scale of each member in the drawings below has been
changed appropriately to sizes that enable each member to be
recognized easily.
First Embodiment
[0132] The first embodiment of the invention is described hereafter
referring to FIGS. 1 to 3.
[0133] The light source device 10 related to the first embodiment
includes a light emitting section 11 and a wavelength selective
element 12.
[0134] The light emitting section 11 includes five light emitting
elements (semiconductor laser: LD) 11a, 11b, 11c, 11d, 11e that
emit laser light.
[0135] Each of the light emitting elements 11a, 11b, 11c, 11d, and
11e is supported by a support member 13.
[0136] The peak wavelengths of light emitted from the light
emitting elements 11a, 11b, 11c, 11d, and 11e substantially
coincide.
[0137] However, the wavelengths may vary slightly, they need not
necessarily coincide perfectly.
[0138] Generally, they may differ by a few nm because of
manufacturing errors in the light emitting elements.
[0139] The wavelength selective element 12 selects a part of the
light W1 of predetermined selective wavelength (approximately 98 to
99%) from the incident laser light (dotted line shown in FIG. 1)
and reflects the laser light including the selective wavelength
toward the light emitting section 11. Thus, the wavelength
selective element 12 functions as a resonator mirror of the light
emitting elements 11a, 11b, 11c, 11d, and 11e, and also allows the
rest of the laser light (dashed and two-dotted line in FIG. 1) W2
to pass through.
[0140] As the wavelength selective element 12, an optical element
such as a hologram having periodic lattices may used.
[0141] The light (solid line shown in FIG. 1) W3 of the fundamental
harmonic emitted from the light emitting section 11 is repetitively
reflected between the light emitting section 11 and the wavelength
selective element 12. After amplification, the amplified light is
emitted from the wavelength selective element 12 as laser light
W2.
[0142] The wavelength selective element 12 passes through light of
different wavelengths, but the wavelength selective element 12
amplifies light of only certain predetermined wavelengths.
[0143] The intensity of amplified light is extremely high compared
to the intensity of light of other wavelengths.
[0144] Thus, the light W2 after passing through the wavelength
selective element 12 can be generally treated as light of a single
wavelength.
[0145] The wavelength of the light W2 is substantially the same as
the selective wavelength of the wavelength selective element 12,
that is, the wavelength of light W1 reflected by the wavelength
selective element 12.
[0146] The wavelength selective element 12 reflects a part
(approximately 98 to 99%) of the light of predetermined selective
wavelength, and thus the remaining light (approximately 1 to 2%)
will be used as output light.
[0147] As shown in FIG. 1, a piezoelectric element (strain
application section) 15 is attached in contact with a first end
face (end face on the side of region E mentioned hereafter) 12c
perpendicular to the incident face 12a of the wavelength selective
element 12 onto which the light emitted from the light emitting
section 11 is incident.
[0148] As the piezoelectric element 15, piezoelectric ceramics and
piezoelectric crystals such as crystal, lead titanate
(PbTiO.sub.3), lead zirconate (PbZrO.sub.3), barium titanate
(BaTiO.sub.3) may be used.
[0149] An absorbing member 16 is provided on a second end face (end
face on the side of the region A mentioned hereafter) 12b opposite
to the first end face 12c of the wavelength selective element, as
shown in FIG. 1.
[0150] The absorbing member 16 is fixed such that the absorbing
member 16 cannot be moved.
[0151] The thickness in the longitudinal direction of the
wavelength selective element 12 of the piezoelectric element 15 is
approximately 0.1 mm.
[0152] However, this number is just an example. This number may
vary depending on the material used for the piezoelectric element
15.
[0153] The piezoelectric element 15 is displaced when voltage is
applied. Strain is caused in the wavelength selective element 12 as
a result of this displacement.
[0154] The piezoelectric element 15 is installed on the first end
face 12c of the wavelength selective element 12. The position of
the absorbing member 16 is fixed.
[0155] Thus, the piezoelectric element 15 will pressurize in the
direction from the piezoelectric element 15 to the absorbing member
16, that is in a direction perpendicular to the central axis
(optical axis) O of the laser light emitted from each of the light
emitting elements 11a, 11b, 11c, 11d, and 11e.
[0156] As a result, strain is generated in the wavelength selective
element 12.
[0157] The magnitude of the strain is maximum on the side of the
first end face 12c on which the piezoelectric element 15 is
installed, and the magnitude of the strain gradually reduces on
moving toward the side of the second end face 12b on which the
absorbing member 16 is installed.
[0158] The selective wavelength of the wavelength selective element
12, that is, the wavelength of light W1 reflected by the wavelength
selective element 12 varies corresponding to this strain.
[0159] The selective wavelength becomes shorter as the strain
increases, and becomes longer with the decrease in the strain
because of the relationship with the refractive index of the
wavelength selective element 12.
[0160] That is, when the piezoelectric element 15 applies pressure,
the selective wavelength on the side of the piezoelectric element
15 shifts to the side of the shorter wavelength compared to the
selective wavelength on the side of the absorbing member 16.
[0161] Here, the regions selected by the light emitted from the
light emitting elements 11a, 11b, 11c, 11d, and 11e (light
selective regions) in one base member that forms the wavelength
selective element 12 are taken as the regions A, B, C, D, and
E.
[0162] However, since regions A, B, C, D, and E are regions on
which the magnitude of the selective wavelength and strain actually
varies gradually and continuously, no physical boundary exists
between these regions.
[0163] The magnitude of the strain is maximum on the side of the
first end face 12c on which the piezoelectric element 15 is
installed, and the magnitude of the strain gradually reduces on
moving toward the side of the second face 12b on which the
absorbing member 16 is installed. Therefore, the magnitude of the
strain becomes maximum in the region E closest to the piezoelectric
element 15. The magnitude of the strain reduces sequentially in the
regions in the order: D, C, B, and A.
[0164] Consequently, the selective wavelength of the wavelength
selective element 12, that is, the wavelength of light W1 reflected
by the wavelength selective element 12 varies corresponding to the
regions A, B, C, D, and E.
[0165] The selective wavelength becomes shorter as the strain
increases and becomes longer as the strain decreases. Therefore,
the selective wavelength becomes shortest in the region E closest
to the piezoelectric element 15, and the selective wavelength
becomes longer sequentially in regions D, C, B and A
respectively.
[0166] That is, if the wavelengths of light W1 reflected by the
regions A, B, C, D, and E of the wavelength selective element 12
are taken as .lamda.1, .lamda.2, .lamda.3, .lamda.4 and .lamda.5,
then .lamda.1>.lamda.2>.lamda.3>.lamda.4>.lamda.5.
[0167] In this way, the wavelength of light W1 reflected by the
wavelength selective element 12 differs according to the region A,
B, C, D, and E. Thus, the reflection of the light is repeated
between the light emitting section 11 and the wavelength selective
element 12, and after amplification, the wavelength of light W2
emitted from the wavelength selective element also differs
according to the region A, B, C, D, and E.
[0168] The wavelength of the light W2 emitted from the wavelength
selective element 12 is substantially identical to the wavelength
of light W1 reflected by the wavelength selective element 12.
[0169] Thus, the wavelengths of light W2 emitted from the regions
A, B, C, D, and E of the wavelength selective element 12 are
.lamda.1, .lamda.2, .lamda.3, .lamda.4 and .lamda.5 respectively,
and also their relationship becomes:
.lamda.1>.lamda.2>.lamda.3>.lamda.4>.lamda.5.
[0170] Since the wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4
and .lamda.5 vary according to the magnitude of the strain, the
values of .lamda.1, .lamda.2, .lamda.3, .lamda.4 and .lamda.5, and
the difference in the magnitude of these values can be adjusted to
the desired values by controlling the piezoelectric element 15.
[0171] Next, a detailed example of the light source device 10
related to the first embodiment is described here.
[0172] First, the light emitting elements 11a, 11b, 11c, 11d, and
11e are semiconductor lasers of red color. Each of the light
emitting elements has a peak wavelength of emitted light of 630
nm.
[0173] These peak wavelengths need not match exactly within the
light emitting elements 11a to the light emitting element 11e. A
slight variation is permitted.
[0174] Generally, they may differ by a few nm because of
manufacturing errors in the light emitting elements.
[0175] At this stage, if the piezoelectric element 15 is controlled
such that the selective wavelengths .lamda.1, .lamda.2, .lamda.3,
.lamda.4, and .lamda.5 in the regions A, B, C, D, and E of the
wavelength selective element 12 become 630 nm, 626 nm, 627 nm, 629
nm, and 628 nm respectively (the difference in the selective
wavelength is 4 nm maximum), then the wavelength of light W2
emitted from the regions A, B, C, D, and E of the wavelength
selective element 12 also become 630 nm, 626 nm, 627 nm, 629 nm,
and 628 nm respectively.
[0176] As described above, if the wavelength selective element 12
having a plurality of light selective regions A, B, C, D, and E
with different selective wavelengths from each other is provided in
one base member in the light source device 10 related to the first
embodiment, the wavelengths of light emitted from each of the
regions A, B, C, D, and E can be made different from each
other.
[0177] Accordingly, the band of light emitted from the wavelength
selective element 12 expands compared to the case in which the
light of the identical wavelength is emitted from all the regions.
Therefore, the coherence of the laser light beams decreases.
[0178] As the result, the light source device 10 with suppressed
speckle noise can be attained.
[0179] Since the wavelength selective element 12 is the same size
as normally used, the device does not increase in size, and the
entire device can be made smaller compared to the conventional
structure in which diffusion elements or exciting devices are used
to reduce the speckle noise.
[0180] The light source device 10 of the invention is small in
size, and can reduce the coherence of the laser light beams, and
can suppress speckle noise.
[0181] In the first embodiment, the peak wavelengths of the light
emitting elements 11a, 11b, 11c, 11d, and 11e were used that
substantially coincided, but light emitting elements in which the
peak wavelengths differ may be actively used.
[0182] That is, the light emitting elements 11a, 11b, 11c, 11d, and
11e may be used in which the peak wavelengths sequentially decrease
in value, and the piezoelectric element 15 may be controlled such
that light of the same length as the peak wavelength of each of the
light emitting element 11a to the light emitting element 11e is
selected in the regions A, B, C, D, and E.
[0183] Also, to facilitate the transmission of strain in the
wavelength selective element 12 by the piezoelectric element 15 to
the desired state, the shape of the wavelength selective element 12
may be made asymmetrical, that is, the cross section area may be
made to reduce from the second end face 12b while moving toward the
first end faces 12c.
[0184] As a detailed example, the maximum difference in the
selective wavelengths in the regions A, B, C, D, and E of the
wavelength selective element 12 was made 4 nm, but if this
difference is within the maximum range of 10 nm, the chromaticity
of light sensed by human beings does not change.
[0185] In this way, by suppressing the difference in selective
wavelengths in the regions A, B, C, D, and E within the maximum
range of 10 nm, for example, by using the light source device 10 in
the image display device, an extremely clear image can be
displayed.
[0186] The piezoelectric element 15 was used as the strain
application section, but it is not limited to this element. For
example, strain gauge or magnetostrictive element may be used.
Second Embodiment
[0187] Next, the second embodiment related to the invention is
described hereafter referring to FIG. 2.
[0188] In each of the embodiments described hereafter, the same
reference numerals are used at locations common to the
configuration of the light source device 10 related to the first
embodiment mentioned above, and explanations are omitted.
[0189] In the light source device 20 related to the second
embodiment, a heat emitting element 21 and a heat absorbing element
22 are provided instead of the piezoelectric element 15 and the
absorbing member 16 of the first embodiment.
[0190] All other points are the same as the first embodiment,
including the descriptive examples and examples of
modification.
[0191] As shown in FIG. 2, the heat emitting element (temperature
variation section) 21 is attached in contact with the second end
face (end face on the side of region A) 12b perpendicular to the
incident face 12a of the wavelength selective element 12 onto which
light emitted from the light emitting section 11 is incident.
[0192] Also, the heat absorbing element 22 is provided on the first
end face (end face on side of the region E) 12c of the wavelength
selective element 12.
[0193] In this way, the heat emitting element 21 is installed in
the second end face 12b of the wavelength selective element 12, and
the heat absorbing element 22 is installed in the first end face
12c. Therefore, the wavelength selective element 12 will be heated
in a perpendicular direction with respect to the central axis O of
the laser light. That is from the side of the heat emitting element
21 toward the side of the heat absorbing element 22.
[0194] A temperature gradient will be generated in the wavelength
selective element 12 such that the temperature gradually decreases
from the heat emitting element 21 toward the heat absorbing element
22.
[0195] That is, in the second embodiment, the temperature of the
wavelength selective element 12 gradually decreases from the region
A toward the region E.
[0196] The wavelength selective element 12 thermally expands due to
heat and its refractive index changes.
[0197] The selective wavelength of the wavelength selective element
12, that is, the wavelength of light W1 reflected by the wavelength
selective element 12 varies corresponding to this thermal
expansion.
[0198] The selective wavelength becomes shorter as the strain
increases, and becomes longer with the decrease in the strain, as
described in the first embodiment.
[0199] The thermal expansion is also considered to be a kind of
strain, therefore, selective wavelength on the side of heat
emitting element 21 with large thermal expansion due to high
temperature shifts toward the long wavelength side compared to the
selective wavelength on the side of the absorbing member 16.
[0200] That is, if the wavelengths in the regions A, B, C, D, and E
of the wavelength selective element 12 are taken as .lamda.1,
.lamda.2, .lamda.3, .lamda.4, and .lamda.5, then
.lamda.1>.lamda.2>.lamda.3>.lamda.4>.lamda.5.
[0201] Thus, the wavelengths of light W2 emitted from the regions
A, B, C, D, and E of the wavelength selective element 12 become
.lamda.1, .lamda.2, .lamda.3, .lamda.4 and .lamda.5 respectively,
and also their relationship becomes:
.lamda.1>.lamda.2>.lamda.3>.lamda.4>.lamda.5.
[0202] In the light source device 20 related to the second
embodiment also, effects similar to the light source device of the
first embodiment can be obtained.
[0203] Temperature can be monitored easily compared to pressure,
and control is also easy, therefore, effects similar to the light
source device of the first embodiment can be more easily
obtained.
[0204] Furthermore, in the second embodiment, if optical element
such as a hologram having periodic lattice is used as the
wavelength selective element 12, then the internal periodic lattice
spacing can be varied easily by applying heat to the wavelength
selective element 12.
[0205] As a result, the coherence of the amplified light beams
emitted from region A, B, C, D, and E of the wavelength selective
element 12 reduces with a simpler configuration, and thus the
speckle noise can be suppressed.
[0206] In the second embodiment, heat emitting element was used as
the temperature variation section, and the wavelength selective
element 12 was heated, but a Peltier element may be used instead of
the heat emitting element.
[0207] Since heating and cooling are possible when a Peltier
element is used, this is especially beneficial when controlling the
selective wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4 and
.lamda.5 in the regions A, B, C, D, and E of the wavelength
selective element 12 to the desired values.
[0208] Moreover, heat may be released by methods such as cooling in
air without using the heat absorbing element 22.
[0209] Also, to control the selective wavelengths .lamda.1,
.lamda.2, .lamda.3, .lamda.4 and .lamda.5, temperature sensors such
as thermistors may be installed in the regions A, B, C, D, and E of
the wavelength selective element 12 and the temperature may be
measured. Depending on the measured temperature, the heating
temperature due to the heat emitting element 21 and the heating
time may be controlled, and the current flowing through the Peltier
element may also be controlled.
Third Embodiment
[0210] Next, the third embodiment related to the invention is
described hereafter referring to FIG. 3.
[0211] The wavelength selective element in the light source device
30 related to the third embodiment differs from the first
embodiment in that a wavelength selective element 33 is made of a
wavelength selective film formed on the substrate 32.
[0212] All other points are the same as the first embodiment,
including the descriptive examples.
[0213] As shown in FIG. 3, the wavelength selective element 33 is
formed on a substrate 32 having optical transparency and the first
film 31a, the second film 31b and the third film 31c are stacked
sequentially from the side of substrate 32.
[0214] Glass, for example, may be used as the substrate 32.
[0215] As the material of the second film 31b, for example,
TiO.sub.2 may be used.
[0216] As the material of the first film 31a and the third film
31c, for example, SiO.sub.2 may be used.
[0217] The type and quantity of films that form the wavelength
selective element 33 may be appropriately selected according to the
desired characteristics.
[0218] Since this point is well-known, details are omitted
here.
[0219] The wavelength selective element 33 is formed so that its
overall thickness becomes smaller by reducing the thickness of the
films 31a, 31b, and 31c, respectively as moving from a first end
33b toward a second end 33c.
[0220] This kind of wavelength selective element 33 may be formed
by oblique deposition.
[0221] The selective wavelength of the wavelength selective element
33, that is, the wavelength of light W1 reflected by the wavelength
selective element 33 varies corresponding to change in thickness of
this film.
[0222] The selective wavelength becomes longer as the thickness of
the film increases. The selective wavelength becomes shorter as the
thickness of the film decreases.
[0223] The thickness of film of the portion through which the laser
light passes, namely J, K, L, M, and N in the regions A, B, C, D,
and E becomes smaller sequentially moving from region A, B, C, D,
and E. Thus, the selective wavelengths .lamda.1, .lamda.2,
.lamda.3, .lamda.4, and .lamda.5 in each region satisfies the
condition:
.lamda.1>.lamda.2>.lamda.3>.lamda.4>.lamda.5.
[0224] Since the wavelengths .lamda.1, .lamda.2, .lamda.3,
.lamda.4, and .lamda.5 vary according to the material, number of
layers, thickness, and so on of the film, the values of .lamda.1,
.lamda.2, .lamda.3, .lamda.4, and .lamda.5, and the difference in
the magnitude of these values can be adjusted to the desired values
by controlling these elements.
[0225] In the light source device 30 related to the third
embodiment also, effects similar to the light source device of the
first embodiment can be obtained.
[0226] Moreover, in the light source device 30 related to the third
embodiment, the selective wavelength can be properly controlled by
adjusting the film thickness, and there is no need for mechanical
controls.
[0227] Consequently, by using a simpler configuration compared to
the first and the second embodiments, the coherence of the light
beams emitted from each region of the wavelength selective element
33 correctly reduces, and the speckle noise can be suppressed.
[0228] In the third embodiment, the peak wavelengths of the light
emitting elements 11a, 11b, 11c, 11d, and 11e that substantially
coincided were used, as described in the first embodiment, but
light emitting elements in which the peak wavelengths differ may be
actively used.
[0229] Also, in the third embodiment, the thickness of the film was
made to gradually reduce from the first end 33b toward the second
end 33c, but the thickness may be changed according to each region
of the wavelength selective element 33.
Fourth Embodiment
[0230] Next, the fourth embodiment related to the invention is
described hereafter referring to FIG. 4.
[0231] The light source device 70 related to the fourth embodiment
differs from the first embodiment in that piezoelectric elements
15a, 15b, 15c, 15d, and 15e are provided for each region A, B, C,
D, and E of the wavelength selective element 12 instead of the
piezoelectric element 15 and the absorbing member 16 provided in
the wavelength selective element 12.
[0232] All other points are the same as the first embodiment,
including the descriptive examples.
[0233] As shown in FIG. 4, the piezoelectric elements (strain
application sections) 15a, 15b, 15c, 15d, and 15e are installed at
a predetermined spacing in each of the regions A, B, C, D, and E on
the surface 12d of the wavelength selective element 12 of the
fourth embodiment.
[0234] Also, damping member may be provided between the adjacent
piezoelectric elements 15a, 15b, 15c, 15d, and 15e so that strain
is not transmitted between the adjacent regions.
[0235] These piezoelectric elements 15a, 15b, 15c, 15d, and 15e may
apply strain to the regions A, B, C, D, and E so as to vary the
magnitude of the strain on the regions A, B, C, D, and E.
[0236] The piezoelectric elements 15a, 15b, 15c, 15d, and 15e are
made similar to the piezoelectric element 15 of the first
embodiment. Therefore, piezoelectric elements are displaced when
voltage is applied, and strain is generated in the wavelength
selective element 12 because of this displacement.
[0237] As shown in FIG. 5A, the wavelength selective element 12 was
controlled in the first embodiment such that the selective
wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4, and .lamda.5 in
the wavelength selective element 12 became successively smaller
when proceeding from region A toward region E.
[0238] As shown in FIG. 5B, the wavelength selective element 12 can
be controlled in the fourth embodiment such that the selective
wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4, and .lamda.5
become an intermittent wavelength distribution (random wavelength
distribution).
[0239] The distribution shown in FIG. 5B is merely an example.
[0240] Thus, in the fourth embodiment, for example, elements in
which peak wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4, and
.lamda.5 of light emitted from the light emitting elements 11a,
11b, 11c, 11d, and 11e are 630 nm, 626 nm, 627 nm, 629 nm, and 628
nm respectively, are used because of manufacturing errors.
[0241] At this stage, the refractive index of each region from A,
B, C, D, and E is changed by controlling the strain in the regions
A, B, C, D, and E of the wavelength selective element 12 by the
piezoelectric elements 15a, 15b, 15c, 15d, and 15e.
[0242] The strain in each region A, B, C, D, and E is controlled
such that the selective wavelengths .lamda.1, .lamda.2, .lamda.3,
.lamda.4, and .lamda.5 in each of the regions A, B, C, D, and E
become 630 nm, 626 nm, 627 nm, 629 nm, and 628 nm respectively.
[0243] In the light source device 70 related to the fourth
embodiment also, the speckle noise can be reduced similar to the
light source device of the first embodiment.
[0244] Moreover, in the fourth embodiment, the degree of freedom of
the output wavelength distribution emitted from the wavelength
selective element 12 can be enhanced because piezoelectric elements
15a, 15b, 15c, 15d, and 15e have been installed to the regions A,
B, C, D, and E, respectively.
[0245] Accordingly, the wavelength of light emitted from light
emitting elements 11a, 11b, 11c, 11d, and 11e and the corresponding
wavelength of light selected for each of the regions A, B, C, D,
and E of the wavelength selective element 12 can be aligned.
[0246] As a result, even if variation exists in the output
wavelength due to manufacturing errors in the light emitting
elements 11a, 11b, 11c, 11d, and 11e, the light utilization
efficiency of light emitted from the wavelength selective element
12 can be enhanced.
[0247] Furthermore, since piezoelectric elements 15a, 15b, 15c,
15d, and 15e have been provided for each of the regions A, B, C, D,
and E, the difference in the selective wavelengths for the regions
A, B, C, D, and E can be increased or decreased regardless of the
figure of 1 nm. Thus, the speckle noise can be reduced more
efficiently.
[0248] Light emitting elements 11a, 11b, 11c, 11d, and 11e that
intentionally emit light of differing wavelengths may also be
used.
[0249] Also, all equal peak wavelengths of light emitted from the
light emitting elements 11a, 11b, 11c, 11d, and 11e may be used
similar to the first embodiment.
[0250] In such a configuration, the speckle noise can be reduced by
controlling the strain in each of the regions A, B, C, D, and E
such that the selective wavelengths of each of the regions A, B, C,
D, and E differ.
[0251] Furthermore, the strain may be controlled using a
piezoelectric element for the light selective regions A, B, C, D,
and E, that is, by taking, for example, two regions together.
[0252] In this configuration also, strain may be applied such that
the wavelengths of light selected by the light selective regions
are different from each other.
[0253] Moreover, Peltier elements (temperature variation sections)
may be provided in each of the regions A, B, C, D, and E instead of
the piezoelectric elements 15a, 15b, 15c, 15d, and 15e.
[0254] Even when Peltier element is used, thermal expansion occurs
by controlling the temperature in the regions A, B, C, D, and E of
the wavelength selective element 12, and the refractive index of
each of the regions A, B, C, D, and E changes, similar to the case
when piezoelectric element is used.
[0255] The temperature in each of the regions A, B, C, D, and E is
controlled such that the selective wavelengths .lamda.1, .lamda.2,
.lamda.3, .lamda.4, and .lamda.5 in each of the regions A, B, C, D,
and E become 630 nm, 626 nm, 627 nm, 629 nm, and 628 nm
respectively.
[0256] Even with this configuration, the speckle noise can be
suppressed, and the light utilization efficiency can be
enhanced.
[0257] Since the temperature in each of the regions A, B, C, D, and
E of the wavelength selective element 12 can be increased and
decreased by using Peltier element as the temperature variation
section, the selective wavelengths of the wavelength selective
element can be matched more accurately with the wavelengths of
light emitted from the light emitting elements 11a, 11b, 11c, 11d,
and 11e.
[0258] The temperature of each of the regions A, B, C, D, and E of
the wavelength selective element 12 may be changed using
electrically heated wire and so on, as the heat emitting element
(temperature variation section) instead of the Peltier element.
Fifth Embodiment
[0259] Next, the fifth embodiment related to the invention is
described hereafter referring to FIG. 6.
[0260] The light source device 80 related to the fifth embodiment
differs from the fourth embodiment in that heat absorbing films
81a, 81b, 81c, 81d, and 81e are provided instead of the
piezoelectric elements 15a, 15b, 15c, 15d, and 15e of the fourth
embodiment.
[0261] All other points are the same as the fifth embodiment,
including the descriptive examples.
[0262] The temperature variation section 85 used in the light
source device 80 includes a laser light source 82 for generating
heat, a mirror 83, and heat absorbing films 81a, 81b, 81c, 81d, and
81e.
[0263] As shown in FIG. 6, the heat absorbing films 81a, 81b, 81c,
81d, and 81e are provided in each of the regions A, B, C, D, and E
on the surface 12d at a predetermined spacing.
[0264] The film thickness of each of the heat absorbing films 81a,
81b, 81c, 81d, and 81e is the same.
[0265] Insulating member may be provided between the adjacent heat
absorbing films 81a, 81b, 81c, 81d, and 81e so that heat is not
transmitted between the adjacent regions A, B, C, D, and E.
[0266] The mirror 83 is used for scanning the laser light emitted
by the laser light source for generating heat toward the heat
absorbing films 81a, 81b, 81c, 81d, and 81e.
[0267] The length of time for which the laser light emitting onto
the heat absorbing films 81a, 81b, 81c, 81d, and 81e is adjusted by
controlling the inclination of the mirror 83.
[0268] As a result, the longer the time for which the laser light
emits, the higher is the temperature of the heat absorbing films
81a, 81b, 81c, 81d, and 81e. Thus, the temperature of the regions
A, B, C, D, and E increases.
[0269] In the fifth embodiment also, the temperature in each of the
regions A, B, C, D, and E of the wavelength selective element 12 is
controlled such that the peak wavelengths of the light emitting
elements 11a, 11b, 11c, 11d, and 11e coincide, similar to the above
described embodiment.
[0270] In the light source device 80 related to the fifth
embodiment also, the speckle noise can be reduced similar to the
light source device of the first embodiment.
[0271] Furthermore, according to the fifth embodiment, the light
utilization efficiency of light emitted from the wavelength
selective element 12 can be enhanced similar to the fifth
embodiment.
[0272] The film thicknesses of the heat absorbing films 81a, 81b,
81c, 81d, and 81e were made the same in the fifth embodiment, but
the film thickness of the heat absorbing films 81a, 81b, 81c, 81d,
and 81e may be made unequal.
[0273] This configuration enables temperature distribution to be
provided in each of the regions A, B, C, D, and E of the wavelength
selective element 12 without varying the scan rate of the mirror
83.
[0274] That is, since the scan rate per scan of the mirror 83 in
the regions A, B, C, D, and E is fixed, mirror 83 can be easily
controlled.
[0275] The heat absorbing films 81a, 81b, 81c, 81d, and 81e were
provided for each of the regions A, B, C, D, and E, but they may be
provided all over the surface 12d of the wavelength selective
element 12.
[0276] Moreover, MEMS mirror may be used as the mirror 83.
Sixth Embodiment
[0277] Next, the sixth embodiment related to the invention is
described hereafter referring to FIG. 7.
[0278] As shown in FIG. 7, the light source device 40 related to
the sixth embodiment, includes a light emitting section 41, a
wavelength conversion element 43, and a wavelength selective
element 42.
[0279] The wavelength conversion element 43 converts the wavelength
of light emitted from the light emitting section 41.
[0280] The wavelength selective element 42 selects and reflects the
wavelength converted by the wavelength conversion element 43.
[0281] The light emitting section 41 includes five light emitting
elements 41a, 41b, 41c, 41d, and 41e that are supported in a linear
shape in the support member 41f.
[0282] The peak wavelengths of light .lamda.0 emitted from the
light emitting element 41a, 41b, 41c, 41d, and 41e substantially
coincide.
[0283] However, the wavelengths may vary slightly, they need not
necessarily coincide perfectly.
[0284] Generally, they may differ by a few nm because of
manufacturing errors in the light emitting elements.
[0285] For example, in the case of a blue laser light source device
that emits blue laser light, the peak wavelength .lamda.0 is 920
nm, in case of a green laser light source device that emits green
laser light, the peak wavelength .lamda.0 is 1060 nm, and in case
of a red laser light source device that emits red laser light, the
peak wavelength .lamda.0 is 1240 nm.
[0286] However, the wavelength mentioned above is merely an
example.
[0287] The wavelength conversion element (second high harmonic
generating element; SHG Second Harmonic Generation) 43 is a
non-linear optical element that converts the incident light into
substantially half the wavelength.
[0288] The light W3 emitted from the light emitting section 41 and
heading toward the wavelength selective element 42 is converted
into light of substantially half the wavelength when the light W3
passes through the wavelength conversion element.
[0289] The wavelength conversion efficiency by the wavelength
conversion element 43 has non-linear characteristics. For example,
the stronger the intensity of laser light incident on the
wavelength conversion element 43, the higher is the conversion
efficiency.
[0290] The conversion efficiency of the wavelength conversion
element 43 is approximately 40% to 50%.
[0291] That is, not all the laser light emitted from the light
emitting section 41 is converted into laser light of the
predetermined wavelength.
[0292] The wavelength conversion element 43 is a sheet in
shape.
[0293] The wavelength conversion element 43 is divided into five
regions P, Q, R, S, and T corresponding to the light emitting
elements 41a, 41b, 41c, 41d, and 41e.
[0294] That is, the regions through which the light emitted from
the light emitting elements 41a, 41b, 41c, 41d, and 41e passes are
taken as P, Q, R, S, and T (light pass-through regions).
[0295] The wavelength conversion element 43 has a polarization
periodic structure corresponding to each of the regions P, Q, R, S,
and T, that is, the polarization has a reversed domain-repetitive
structure with respect to each other.
[0296] When the light in the polarization periodic structure passes
through, the wavelength of the incident light will be
converted.
[0297] The width in the direction of the central axis of the laser
light (hereafter referred to as "pitch") of each domain of the
regions P, Q, R, S, and T of the wavelength conversion element 43
is .LAMBDA.1, .LAMBDA.2, .LAMBDA.3, .LAMBDA.4, and .LAMBDA.5.
[0298] Pitch .LAMBDA.1, .LAMBDA.2, .LAMBDA.3, .LAMBDA.4, and
.LAMBDA.5 are mutually different, and
.LAMBDA.1>.LAMBDA.2>.LAMBDA.3>.LAMBDA.4>.LAMBDA.5.
[0299] This kind of polarization periodic structure can be
produced, for example, by applying the manufacturing method
disclosed in the Japanese Unexamined Patent Application, First
Publication No. H04-19719.
[0300] That is, first a striped-shape electrode patterns with
regions having electrodes and regions having no electrodes
alternately disposed along the direction of the central axis O of
the laser light are formed on the substrate made of a non-linear
ferrodielectric material (such as LiTaO.sub.3).
[0301] At this stage, the width of each electrode pattern and the
spacing of electrode patterns are optimized such that the pitch of
each domain in the regions P, Q, R, S, and T become .LAMBDA.1,
.LAMBDA.2, .LAMBDA.3, .LAMBDA.4, and .LAMBDA.5.
[0302] That is, the width and spacing of the electrode patterns
differ in each of the regions P, Q, R, S, and T.
[0303] Next, a polarization periodic structure as shown in FIG. 7
can be obtained by applying voltage in pulse form on these
electrode patterns.
[0304] After forming the polarization periodic structure in this
way, commonly, the electrode patterns are removed, but they may
also be retained as they are.
[0305] In this way, the wavelength conversion element 43 has a
polarization reversed structure with differing period (pitch) in
each of the regions P, Q, R, S, and T.
[0306] Accordingly, among the various wavelength components
included in light of peak wavelength .lamda.0, the components of
wavelength .lamda.01, .lamda.02, .lamda.03, .lamda.04, and
.lamda.05 that differ slightly from each other in the light passing
through the regions P, Q, R, S, and T are subjected to conversion
action, and are converted into wavelengths .lamda.1, .lamda.2,
.lamda.3, .lamda.4, and .lamda.5 respectively that differ slightly
from each other.
[0307] If the example of wavelength of blue laser light source
device is taken, then light near the wavelength of .lamda.01=920
nm, .lamda.02=918 nm, .lamda.03=916 nm, .lamda.04=914 nm,
.lamda.05=912 nm from light of peak wavelength .lamda.0=920 nm
emitted from the light emitting elements 41a, 41b, 41c, 41d, and
41e respectively is converted into light of wavelength .lamda.1=460
nm, .lamda.2=459 nm, .lamda.3=458 nm, .lamda.4=457 nm, and
.lamda.5=456 nm.
[0308] Similarly, if the example of wavelength of green laser light
source device is taken, then light near the wavelength of
.lamda.01=1060 nm, .lamda.02=1058 nm, .lamda.03=1056 nm,
.lamda.04=1054 nm, .lamda.05=1052 nm from light of peak wavelength
.lamda.0=1060 nm emitted from the light emitting elements 41a, 41b,
41c, 41d, and 41e respectively is converted into light of
wavelength .lamda.1=530 nm, .lamda.2=529 nm, .lamda.3=528 nm,
.lamda.4=527 nm, and .lamda.5=526 nm.
[0309] Also similarly, if the example of wavelength of red laser
light source device is taken, then light near the wavelength of
.lamda.01=1240 nm, .lamda.02=1238 nm, .lamda.03=1236 nm,
.lamda.04=1234 nm, .lamda.05=1232 nm from light of peak wavelength
of 1240 nm emitted from the light emitting elements 41a, 41b, 41c,
41d, and 41e respectively is converted into light of wavelength
.lamda.1=620 nm, .lamda.2=619 nm, .lamda.3=618 nm, .lamda.4=617 nm,
and .lamda.5=616 nm.
[0310] However, the wavelength mentioned above is merely an
example.
[0311] The wavelength selective element 42 selects only the laser
light W1 (that is, light of wavelength .lamda.01, .lamda.02,
.lamda.03, .lamda.04, and .lamda.05) that has not been converted
into the predetermined wavelengths .lamda.1, .lamda.2, .lamda.3,
.lamda.4, and .lamda.5 by the wavelength conversion element 43,
reflects the selected laser light toward the light emitting section
41, and passes through the remaining laser light.
[0312] The structure of the wavelength selective element 42 is
similar to that in the first embodiment. The piezoelectric element
15 is provided on the first end face (end face on the side of the
region E) 42c and an absorbing member 16 is provided on the second
end face (end face on the side of region A) 42b.
[0313] The piezoelectric element 15 is controlled such that the
wavelengths .lamda.01, .lamda.02, .lamda.03, .lamda.04, and
.lamda.05 of laser light that have not been converted in the
regions P, Q, R, S, and T, and the wavelengths of light selected in
the regions A, B, C, D, and E of the wavelength selective element
have the same values.
[0314] That is, in case of a blue laser light source device, for
example, the piezoelectric element 15 is controlled such that the
wavelengths of light reflected in the regions A, B, C, D, and E
become 920 nm, 918 nm, 916 nm, 914 nm, and 912 nm,
respectively.
[0315] In case of green laser light source device, for example, the
piezoelectric element 15 is controlled such that the wavelengths of
light reflected in the regions A, B, C, D, and E become 1060 nm,
1058 nm, 1056 nm, 1054 nm, and 1052 nm, respectively.
[0316] In case of red laser light source device, for example, the
piezoelectric element 15 is controlled such that the wavelengths of
light reflected in the regions A, B, C, D, and E become 1240 nm,
1238 nm, 1236 nm, 1234 nm, and 1232 nm, respectively.
[0317] However, the wavelength mentioned above is merely an
example.
[0318] The light W1 (dotted line shown in FIG. 7) reflected by the
wavelength selective element 42 passes through the wavelength
conversion element 43 again, and returns to the light emitting
elements 41a, 41b, 41c, 41d, and 41e.
[0319] A part of the light returned to the light emitting elements
41a, 41b, 41c, 41d, and 41e is absorbed and becomes heat, but most
of the light is used as energy for emission, and is reflected
within the light emitting elements 41a, 41b, 41c, 41d, and 41e, and
again emitted from the light emitting elements 41a, 41b, 41c, 41d,
and 41e and so on, and is thus effectively used.
[0320] On the other hand, the light W2 (dashed and two-dotted line
in FIG. 7) converted into wavelengths .lamda.1, .lamda.2, .lamda.3,
.lamda.4 and .lamda.5 passing through the wavelength selective
element 42 by the wavelength conversion element 43 passes through
the wavelength selective element 42.
[0321] As described above, the light W3 emitted from the light
emitting section 41 is repeatedly reflected between the light
emitting section 41 and the wavelength selective element 42, while
the converted light W2 (dashed and two-dotted line in FIG. 7)
converted into the predetermined wavelength is emitted from the
wavelength selective element 42.
[0322] That is, although the operation of the wavelength selective
element 42 differs slightly compared to the wavelength selective
elements 12 and 33 of the first to the third embodiments, the
wavelength selective element 42 has the function of operation as a
resonator mirror of the light emitting elements 41a, 41b, 41c, 41d,
and 41e.
[0323] By varying the pitch of the domain in the regions P, Q, R,
S, and T in the light source device 40 related to the sixth
embodiment, and by combining the wavelength conversion element 43
that enables conversion of differing wavelengths .lamda.1,
.lamda.2, .lamda.3, .lamda.4 and .lamda.5, and the piezoelectric
element 15 including the light selective regions A, B, C, D, and E
of differing selective wavelengths, the wavelength of light emitted
from the wavelength selective element 42 can be made to differ from
each other.
[0324] Accordingly, the band of light emitted from the wavelength
selective element 12 expands compared to the case in which the
light of the same wavelength is emitted from all the regions.
Therefore, the coherence of the laser light beams decreases.
[0325] The result is that light source device 40 with suppressed
speckle noise can be attained.
[0326] Since the wavelength conversion element 43 and the
wavelength selective element 42 are the same size as normally used,
the device does not increase in size, and the entire device can be
made smaller compared to the conventional device in which diffusion
elements or exciting devices were used to reduce the speckle
noise.
[0327] The light source device 40 of the invention is small in
size, and can reduce the coherence of the laser light beams, and
can suppresses speckle noise.
[0328] In the sixth embodiment, the peak wavelengths of a plurality
of light emitting elements 41a, 41b, 41c, 41d, and 41e that
substantially coincided were used, but light emitting elements in
which the peak wavelengths differ may be actively used.
[0329] That is, the piezoelectric element 15 may be controlled such
that the light emitting elements 41a, 41b, 41c, 41d, and 41e is
used so that each of the peak wavelengths becomes .lamda.01,
.lamda.02, .lamda.03, .lamda.04, and .lamda.05, and such that light
of wavelength same as the peak wavelength of the light emitting
elements 41a, 41b, 41c, 41d, and 41e are selected in the regions A,
B, C, D, and E.
[0330] In this way, by coinciding the peak wavelengths of the light
emitting elements 11a, 11b, 11c, 11d, and 11e, and the selective
wavelengths in the regions A, B, C, D, and E of the wavelength
selective element 42, the light utilization efficiency can be
enhanced.
[0331] By providing the piezoelectric element 15 only on the first
end face 12c of the wavelength selective element 42 in the sixth
embodiment, the selective wavelength gradually increases in length
on proceeding from the side of the piezoelectric element 15 toward
the side of the absorbing member 16. However, as shown in the
fourth embodiment, individual piezoelectric elements can be
provided in each region of the wavelength selective element, and
the strain in each of these regions may be controlled.
[0332] Moreover, as shown in the fifth embodiment, the temperature
of each region may also be controlled by heat absorbing film.
[0333] Also, to facilitate the transmission of strain in the
wavelength selective element 42 by the piezoelectric element 15 to
the desired state, the shape of the wavelength selective element 42
may be made asymmetrical, that is, the cross section area may be
made to reduce from the second end face 42b while moving toward the
first end face 42c.
[0334] As a detailed example, the maximum difference in the
wavelengths of light W2 emitted from the regions A, B, C, D, and E
was made 4 nm, but if this difference is within the maximum range
of 10 nm, the chromaticity of light sensed by human beings does not
change.
[0335] In this way, by suppressing the difference in wavelengths of
light emitted from the regions A, B, C, D, and E within the maximum
range of 10 nm, for example, by using the light source device 40 in
the image display device, an extremely clear image can be
displayed.
[0336] The piezoelectric element 15 was used as the strain
application section, but it is not limited to this element; for
example, a strain gauge or magnetostrictive element may be
used.
Seventh Embodiment
[0337] Next, the seventh embodiment related to the invention is
described hereafter referring to FIG. 8.
[0338] The light source device 50 related to the seventh embodiment
differs from the sixth embodiment in that the pitch of the domain
of the wavelength conversion element 51 is different and a Peltier
element 52 is provided.
[0339] All other points are the same as the sixth embodiment,
including the descriptive examples and examples of
modification.
[0340] In the description of the seventh embodiment, the same
reference numerals are used at locations common to the
configuration of the light source device 40 related to the sixth
embodiment mentioned above, and explanations are omitted.
[0341] The pitches .LAMBDA.1, .LAMBDA.2, .LAMBDA.3, .LAMBDA.4, and
.LAMBDA.5 of the domain of polarization periodic structure in the
wavelength conversion element 43 of the sixth embodiment differ
from each other, and their values reduce sequentially and
gradually, but in the wavelength conversion element 51 of the
seventh embodiment, the pitches .LAMBDA.1, .LAMBDA.2, .LAMBDA.3,
.LAMBDA.4, and .LAMBDA.5 remain substantially the same when the
operation due to the Peltier element 52 described later, is not
received.
[0342] In this way, even wavelength conversion element 51 with
equal pitches .LAMBDA.1, .LAMBDA.2, .LAMBDA.3, .LAMBDA.4, and
.LAMBDA.5 of the domain can be produced according to the method
described in the sixth embodiment.
[0343] All the widths and the spacings of the electrode patterns
used for applying voltage in pulse form in the regions P, Q, R, S,
and T, may be made the same during the manufacturing process
described in the sixth embodiment.
[0344] The Peltier element (temperature variation section) 52 is
attached in contact with a first end face (end face on the side of
region P) 51d perpendicular to the incident face 51c onto which the
light emitted from the light emitting section 41 of the wavelength
conversion element 51 is incident.
[0345] The Peltier element 52 is used to apply an appropriate
temperature gradient to the wavelength conversion element 51.
[0346] The temperature gradient should be controlled such that
light W3 emitted from the light emitting elements 41a, 41b, 41c,
41d, and 41e in each of the regions P, Q, R, S, and T of the
wavelength conversion element is converted into the desired
wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4 and
.lamda.5.
[0347] The Peltier element 52 is controlled so as to obtain the
appropriate temperature gradient, and the Peltier element 52
heats/cools the wavelength conversion element 51.
[0348] The Peltier element 52 is controlled using the temperature
sensors 53a, 53b, 53c, 53d, and 53e installed for each of the
regions P, Q, R, S, and T of the incident face 51 c of the
wavelength conversion element 51.
[0349] That is, the current flowing in the Peltier element 52 is
controlled according to the temperature measured by the temperature
sensors 53a, 53b, 53c, 53d, and 53e.
[0350] These temperature sensors 53a, 53b, 53c, 53d, and 53e are
installed at positions avoiding the light W3 incident on the
wavelength conversion element 51 and the path of the light W1 that
returns from the wavelength conversion element 51, and are
configured such that no effect is caused on these light beams.
[0351] Here, the temperature gradient applied by the Peltier
element 52 is controlled such that its temperature reduces
gradually from the side of the first end face 51d (side of region
P) on which the Peltier element 52 of the wavelength conversion
element 51 is installed toward a second end face 51 a on the
opposite side of the first end face 51d (side of region T).
[0352] That is, temperature gradient that varies gradually from
high temperature to low temperature is applied in a direction
perpendicular to the central axis O of the incident laser light in
the wavelength conversion element 51.
[0353] The refractive index of the wavelength conversion element 51
changes according to this temperature gradient, and the domain
pitch changes due to the thermal expansion.
[0354] The light that has passed through the regions P, Q, R, S,
and T receives the effect of the domain pitch change and the change
in the refractive index. Among the various wavelength components
included in the light of peak wavelength .lamda.0, the components
of wavelength .lamda.01, .lamda.02, .lamda.03, .lamda.04, and
.lamda.05 that differ slightly from each other are affected by the
conversion action, and these components are converted into
wavelength .lamda.1, .lamda.2, .lamda.3, .lamda.4 and .lamda.5,
which differ slightly from each other.
[0355] In the light source device 50 related to the seventh
embodiment also, effects similar to the light source device of the
sixth embodiment can be obtained.
[0356] In the light source device 50 related to the seventh
embodiment, the internal structure of the wavelength conversion
element 51 is changed by applying temperature gradient with the
Peltier element 52 by using wavelength conversion element 51 in
which the domain pitch .LAMBDA.1, .LAMBDA.2, .LAMBDA.3, .LAMBDA.4,
and .LAMBDA.5 are equal to each other.
[0357] Accordingly, the pitch .LAMBDA.1, .LAMBDA.2, .LAMBDA.3,
.LAMBDA.4, and .LAMBDA.5 need not be controlled strictly. Thus, the
manufacturing cost of the wavelength conversion element 51 can be
reduced, and as a consequence, the manufacturing cost of the light
source device 50 can be reduced.
Eighth Embodiment
[0358] Next, the eighth embodiment related to the invention is
described hereafter referring to FIG. 9.
[0359] The light source device 55 related to the eighth embodiment
differs from the seventh embodiment in that Peltier elements 52a,
52b, 52c, 52d, and 52e are provided for each region P, Q, R, S, and
T of the wavelength conversion element 51 instead of the Peltier
element 52 and the temperature sensors 53a, 53b, 53c, 53d, and 53e,
and the use of the wavelength selective element 12 of the fourth
embodiment.
[0360] All other points are the same as the seventh embodiment,
including the descriptive examples.
[0361] Peltier elements (temperature variation sections) 52a, 52b,
52c, 52d, and 52e are installed at a predetermined spacing in each
of the regions P, Q, R, S, and T on the surface 51b in the
wavelength conversion element 51 of the eighth embodiment, as shown
in FIG. 9.
[0362] Insulating member may be provided between the adjacent
Peltier elements 52a, 52b, 52c, 52d, and 52e so that heat is not
transmitted between the adjacent regions.
[0363] With these Peltier elements 52a, 52b, 52c, 52d, and 52e, the
temperature is can be controlled so as to vary the temperature of
each the regions P, Q, R, S, and T.
[0364] As shown in FIG. 5A, the wavelength conversion element 51
was controlled in the seventh embodiment such that the selective
wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4, and .lamda.5 in
the wavelength conversion element 51 became successively smaller
when proceeding from region P toward region T.
[0365] As shown in FIG. 5B, the wavelength conversion element 51
can be controlled in the eighth embodiment such that the conversion
wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4, and .lamda.5
become an intermittent wavelength distribution (random wavelength
distribution).
[0366] Thus, in the eighth embodiment, for example, elements in
which peak wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4, and
.lamda.5 of light emitted from the light emitting elements 41a,
41b, 41c, 41d, and 41e are 630 nm, 626 nm, 627 nm, 629 nm, and 628
nm, respectively, are used because of manufacturing errors.
[0367] At this stage, thermal expansion occurs and the refractive
index of each region from P, Q, R, S, and T changes by controlling
the temperature of the regions P, Q, R, S, and T of the wavelength
conversion element 51 by the Peltier elements 52a, 52b, 52c, 52d,
and 52e.
[0368] The temperature in each of the regions P, Q, R, S, and T is
controlled such that the conversion wavelengths .lamda.1, .lamda.2,
.lamda.3, .lamda.4, and .lamda.5 in each of the regions A, B, C, D,
and E become 630 nm, 626 nm, 627 nm, 629 nm, and 628 nm,
respectively.
[0369] In the light source device 55 related to the eighth
embodiment also, the speckle noise can be reduced similar to the
light source device of the seventh embodiment.
[0370] Moreover, in the eighth embodiment, the degree of freedom of
the output wavelength distribution emitted from the wavelength
conversion element 51 can be enhanced because Peltier elements 52a,
52b, 52c, 52d, and 52e have been installed to the regions P, Q, R,
S, and T, respectively.
[0371] Accordingly, the wavelength of light emitted from light
emitting elements 41a, 41b, 41c, 41d, and 41e and the corresponding
wavelength of light that converts each of the regions P, Q, R, S,
and T of the wavelength conversion element 51 can be aligned.
[0372] As a result, even if variation exists in the output
wavelength due to manufacturing errors and so on in the light
emitting elements 41a, 41b, 41c, 41d, and 41e, the light
utilization efficiency of light emitted from the wavelength
conversion element 51 can be enhanced.
[0373] Furthermore, since the selective wavelength can be changed
in each of the regions A, B, C, D, and E for the wavelength
selective element also, the wavelengths corresponding to the
wavelength conversion element 51 and the wavelength selective
element 12 can also be aligned.
[0374] As a result, the light utilization efficiency can be
enhanced.
[0375] Furthermore, since Peltier elements 52a, 52b, 52c, 52d, and
52e have been provided for each of the regions P, Q, R, S, and T,
the difference in the selective wavelengths for the regions P, Q,
R, S, and T can be increased or decreased regardless of the figure
of 1 nm. Thus, the speckle noise can be reduced more
efficiently.
[0376] Instead of the Peltier elements 52a, 52b, 52c, 52d, and 52e,
and heat emitting elements (temperature variation sections, such as
electrically heated wire) or piezoelectric elements (strain
application sections) may be used.
[0377] With this configuration also, each region from P, Q, R, S,
and T can be individually controlled similar to the case in which
they are used in the wavelength selective element 12, therefore,
the domain pitch of each region from P, Q, R, S, and T may be
changed and the conversion wavelength can be changed.
[0378] Moreover, similar to the wavelength selective element shown
in FIG. 6 of the fifth embodiment, heat absorbing film may be
provided in each region from P, Q, R, S, and T of the surface 51b
of the wavelength conversion element 51.
[0379] With this configuration also, the length of time for which
the laser light emits on the heat absorbing film is adjusted
similar to the fifth embodiment.
[0380] As a result, the domain pitch changes due to thermal
expansion since the temperature of each region from P, Q, R, S, and
T changes in the wavelength conversion element 51.
[0381] Consequently, the light utilization efficiency can be
enhanced by matching the domain pitch of the wavelength conversion
element 51 with the output wavelength of the light emitting
elements 41a, 41b, 41c, 41d, and 41e.
[0382] Furthermore, the temperature may be controlled using a
Peltier element for a plurality of light selective regions P, Q, R,
S, and T of the wavelength conversion element 51, that is, by
taking, for example, two regions together.
[0383] In this configuration also, the temperature may be
controlled such that the wavelengths of light selected by the light
selective regions P, Q, R, S, and T are mutually different.
[0384] Moreover, in this embodiment, the wavelength selective
element 12 shown in the fourth embodiment was used, but the
wavelength selective elements shown in the first, the second, the
third, and the fifth embodiments may be used.
Ninth Embodiment
[0385] Next, the ninth embodiment related to the invention is
described hereafter referring to FIG. 10.
[0386] The light source device 60 related to the ninth embodiment
differs from the seventh embodiment in that electrodes (voltage
application sections) 65a, 65b, 65c, 65d, and 65e are provided on
the surface 61a including regions P, Q, R, S, and T of the
wavelength conversion element 61 instead of the Peltier element
52a, 52b, 52c, 52d, and 52e.
[0387] All other points are the same as the seventh embodiment,
including the descriptive examples and examples of
modification.
[0388] In the wavelength conversion element 61 of the ninth
embodiment, electrodes in sheet form 65a, 65b, 65c, 65d, and 65e
are provided in the regions P, Q, R, S, and T on the surface 61a
such that the a specified spacing is maintained with the adjacent
electrodes.
[0389] The voltage is applied to each of these electrodes 65a, 65b,
65c, 65d, and 65e so that the voltage of each electrodes 65a, 65b,
65c, 65d, and 65e are different from each other. Thereby, the
temperature in each of these regions is different according to the
voltage applied.
[0390] The refractive index in each of the regions P, Q, R, S, and
T of the wavelength conversion element 61 varies according to this
temperature difference, and the domain pitch changes due to the
thermal expansion.
[0391] The voltage applied to the electrodes 65a, 65b, 65c, 65d,
and 65e is controlled such that the temperature reduces gradually
on going from region P to region T, similar to the seventh
embodiment.
[0392] Only electrodes 65a, 65b, 65c, 65d, and 65e formed on the
surface 61a are shown in FIG. 10, but on the surface on the
opposite side of the surface 61a, five electrodes are formed
corresponding to the electrodes 65a, 65b, 65c, 65d, and 65e. The
regions P, Q, R, S, and T are sandwiched between these pairs of
electrodes, and specified voltage is applied on each of the regions
P, Q, R, S, and T.
[0393] In the light source device 60 related to the ninth
embodiment also, effects similar to the light source device of the
seventh embodiment can be obtained.
[0394] Moreover, in the light source device 60 related to the ninth
embodiment, a different voltage can be applied to each of the
regions P, Q, R, S, and T. Therefore, accurate controls for
conversion characteristics can be performed for each region.
[0395] Also, the domain pitch of the regions P, Q, R, S, and T
corresponding to the output wavelengths can be changed when the
wavelengths of light emitted from the light emitting elements 41a,
41b, 41c, 41d, and 41e are different since the domain pitch can be
changed according to regions P, Q, R, S, and T of the wavelength
conversion element 61.
[0396] As a result, the light utilization efficiency in the
wavelength conversion element can be enhanced.
Tenth Embodiment
[0397] Next, the tenth embodiment related to the invention is
described hereafter referring to FIG. 11.
[0398] The image display device 100 provided in the light source
device 10 of the first embodiment mentioned above, is described
hereafter.
[0399] The case which is a portion of the image display device 100
is omitted in FIG. 11 for simplicity.
[0400] In the image display device 100, the light source device 10
of the first embodiment mentioned above is used as the red laser
light source (light source device) 101R that emits red light, and
the light source device 40 of the sixth embodiment mentioned above
is used as the green laser light source (light source device) 101G
that emits green light and blue light, and as the blue laser light
source (light source device) 101B.
[0401] The image display device 100 includes liquid crystal light
valves (light modulating device) 104R, 104G, 104B, a cross dichroic
prism (colored light synthesizing device) 106, and a projection
lens (projection device) 107.
[0402] The liquid crystal light valves 104R, 104G, 104B modulate
the laser light emitted from each of the laser light sources 101R,
101G, and 101B. The cross dichroic prism 106 synthesizes and leads
the light emitted from the liquid crystal light valves 104R, 104G
and 104B to a projection lens 107. The projection lens 107 projects
the images formed by the liquid crystal light valves 104R, 104G,
and 104B on a screen 110.
[0403] Also, in the image display device 100, in order to
uniformize the luminance distribution of laser light emitted from
the laser light sources 101R, 101G, 101B, uniformizing optical
systems 102R, 102G, 102B are installed more downstream side of the
light path than the laser light sources 101R, 101G, and 101B. The
liquid crystal light valves 104R, 104G and 104B are illuminated by
the light with uniformized luminance distribution.
[0404] For example, the uniformizing optical systems 102R, 102G,
and 102B may be made of hologram 102a and field lens 103b.
[0405] Light in three colors modulated by each of the liquid
crystal light valves 104R, 104G and 104B are made incident onto the
cross dichroic prism 106.
[0406] This cross dichroic prism 106 is formed by affixing together
four rectangular prisms. On its inner surface, dielectric
multilayered film that reflects red colored light and dielectric
multilayered film that reflects blue colored light are disposed in
a cross shape.
[0407] Light of three colors are synthesized by these dielectric
multilayered films, and light expressing colored images is
formed.
[0408] Moreover, the synthesized light is projected on the screen
110 by the projection lens 107, which is the projection optical
system, and an enlarged image is displayed.
[0409] In the image display device 100 of the tenth embodiment, the
light emitted from the red laser light source 101R, the green laser
light source 101G, and the blue laser light source 101B is light
with reduced coherence. Thus, the projected light from the
projection lens 107 is light with suppressed speckle noise.
[0410] Accordingly, a satisfactory image can be displayed on the
screen 110.
[0411] The green and blue laser light sources 101G and 101B in the
image display device of the tenth embodiment has been described as
using the light source device 40 of the sixth embodiment, but light
source device of other embodiments may also be used.
[0412] At this stage, light source device of different embodiments
may be used in each of the light source device 101R, 101G, and 101B
respectively, or light device of the same embodiment may be
used.
[0413] Transmissive-type liquid crystal light valve was used as the
light modulating device, but light valves other than liquid crystal
type may also be used, and reflective-type light valves may also be
used.
[0414] Examples of these light valves are reflective type liquid
crystal light valves and digital micro-mirror devices.
[0415] The configuration of the projection optical system may be
appropriately changed to suite the type of light valves used.
[0416] The light source device 10 to 80 of the first to the sixth
embodiments may also be used in scanning type image display
device.
[0417] An example of such an image display device is shown in FIG.
12.
[0418] The image display device 200 shown in FIG. 12 includes the
light source device 10 of the first embodiment, an MEMS mirror
(scanning section) 202 that scans light emitted from the light
source device 10 onto the direction of the screen 210, and a
condenser lens 203 that concentrates the light emitted from the
light source device 10 onto the MEMS mirror 202.
[0419] By moving the MEMS mirror 202, the light emitted from the
light source device 10 is led so as to scan in the horizontal and
vertical directions on the screen 210.
[0420] To display color images, the plurality of light emitting
elements that constitute the light emitting section 11 may be
formed by a combination of light emitting elements having red,
green and blue peak wavelengths.
[0421] Note that the scope of the skill of the invention is not
limited to the embodiment mentioned above, and various changes may
be effected to the invention without departing from the spirit and
scope of the invention.
[0422] For example in the sixth, the seventh and the ninth
embodiments, wavelength selective element 42 provided with a
construction similar to the first embodiment was used, but instead,
the wavelength selective element provided with a construction
similar to the second, the third the fourth and the fifth
embodiments may be used.
[0423] The wavelength selective elements 12, 33, and 42 may have
different selective wavelengths for each light selective region.
They need not reduce sequentially as mentioned above.
[0424] Also, the same holds good for the wavelength conversion
element 43, 51, and 61.
[0425] Short surface emitting laser or surface emitting laser may
be used for the light emitting element.
* * * * *